Not Applicable
Not Applicable
1. Field of the Invention
This invention is in the field of equipment used to install a liner in a well bore.
2. Background Art
It is common to install a liner pipe in a well bore, and thereafter to pump various fluids, such as cement slurry, downhole through the liner pipe. Typically, the cement slurry exits the lower end of the liner pipe and rises into the annular space between the liner pipe and the well bore or the casing. In conjunction with this type of pumping operation, it is also common to pump a wiper plug through the liner pipe behind the cement slurry, to wipe down the walls of the liner pipe and to separate the cement slurry from other fluids subsequently pumped through the liner pipe.
In performing this type of operation, it is typical to lower the wiper plug and the liner pipe on a workstring, to pump the cement slurry through the workstring and the wiper plug, and then to release the wiper plug from the workstring to be pumped further downhole through the liner pipe, behind the slurry. It is desirable to be able to securely fasten the wiper plug to the workstring, to reliably release the wiper plug from the workstring, and to positively detect release of the wiper plug from the workstring. It is also desirable to latch the wiper plug to the workstring in such a way that a backup method of releasing the wiper plug is available, in the event of failure of the first method of release.
This invention includes a method and apparatus for attaching a wiper plug to a workstring and for reliably, and detectably, releasing the wiper plug from the workstring. The wiper plug can be attached to the workstring, for example, by latching a collet onto a grooved latch ring, with the collet being captured or locked into place in a groove on the outer surface of the latch ring by a sleeve which is shifted over the collet fingers. Similarly, the collet could latch into a groove on the inner surface of a latch ring, and the collet could be locked into place by a sleeve which is shifted inside the collet fingers. The collet can be attached to the workstring and the latch ring attached to the wiper plug, or vice versa. The sleeve can be mounted to the workstring or to the wiper plug, and the sleeve can be designed to shift either longitudinally or rotationally, or a combination thereof The sleeve is held in place by a shearable device, such as a shear pin. A hydraulic cylinder is established between the sleeve and the workstring, for example, with a fluid port being provided in the workstring to pressurize the hydraulic cylinder.
With the wiper plug latched to the workstring, and with the collet locked in place by the sleeve, the workstring is lowered into a well bore to a desired location. When it is desired to release the wiper plug, a pumpable plug is pumped downhole through the workstring to land in, and latch to, the wiper plug, below the fluid port. This increases pressure in the hydraulic cylinder to a predetermined level, detectable at the well site, at which the shear pin shears, releasing the sleeve to be shifted away from the collet by the hydraulic cylinder. This shifting of the sleeve releases the collet to flex, allowing the latch ring to pull free from the collet, thereby disengaging the wiper plug from the workstring, assisted by hydraulic pressure against the pumpable plug, which bears downwardly on the wiper plug. The wiper plug and the pumpable plug then continue downhole. Release of the wiper plug results in a sharp drop in the fluid pressure detected at the well site, giving a positive indication that the wiper plug has been released.
In the event that the sleeve jams, or the latch ring becomes jammed in the collet, preventing the release of the wiper plug as described above, a continued increase in pressure will be detected at the well site. When the pressure reaches a second, higher, level, a rupture disk ruptures, establishing flow from the interior of the workstring to the annular space around the workstring, thereby applying hydraulic pressure directly to the outer portion of the upstream end of the wiper plug. The exertion of hydraulic pressure against this increased surface of the wiper plug can then shear a shearable device on the collet or the latch ring, such as a shearable link, to release the wiper plug from the workstring. This release can then be detected at the well site, as a sharp drop in workstring pressure.
The novel features of this invention, as well as the invention itself, will be best understood from the attached drawings, taken along with the following description, in which similar reference characters refer to similar parts, and in which: